Function Tk_UnderlineChars 

pub unsafe extern "C" fn Tk_UnderlineChars(
    display: *mut Display,
    drawable: Drawable,
    gc: GC,
    tkfont: Tk_Font,
    source: *const c_char,
    x: c_int,
    y: c_int,
    firstByte: c_int,
    lastByte: c_int,
)